General:
In this game anyone can make magic items provided they meet the requirements of being proficient with Arcana, proficiency with the respected tool, the appropriate level, having a recipe of that item and a week to dedicate to crafting that item. There are arguments of some tools that require the use of two tools but for simplicity we are going to make those to lean towards one or the other or if it's in the middle, then it comes up as either or.
Recipes:
Now adding a bit of complexity lets ask the question of how your character knows how to make that one or those magic items. We simplify this with your character studying about the formulas of the magic within that week and applying the effect within a safe, slow practice that includes the aid of Strixhaven's Faculty member(s) guiding you. After completing the week, you have successfully crafted your recipe. Once this recipe (of what ever item your character went for) is complete you can now make copies of that item to give to your friends, your self or sell on the market. If you are creating consumables then the character makes two instead of one.
Rarities:
For this we are using the rarity as a complexity. The higher the rarity the more the magic formula shows range of difficulty. This can range in Quandrix arcane circuitry formula to be incorrect, Prismari's balance of expression and perfection to be not a proper setup, Lorehold's history of the structure to be missing vital information, Silverquill not finding the correct wording to shape the flow of arcane, or Witherbloom's lacking proper ingredients substance for the arcane formula of growth or decay. As you level up, you gain understanding, the items become unlocked for you to make recipes and ability to craft them.
Level 1-4 = Common/Uncommon
Level 5-10 = Rare
Level 11-16 = Very Rare
Shops:
Purchasing:
With this setting magic items are abundant to players so to simplify and counter balance assume all magic item for purchasing are at max value unless they are consumables then treat those at half value as "Xanathar's Guide to Everything" suggests. If players are looking to make deals they can play the haggle game with the Referee to get a discount. The prices becomes referee dependent.
Common = 10 Platinum Pieces
Uncommon = 50 Platinum Pieces
Rare = 500 Platinum Pieces
Very Rare = 5,000 Platinum Pieces
Selling:
To provide a simplified challenge to the players, they do have to compete with other venders and students so player's character should sell their crafted items at half value or play the haggle game with the Referee to convince a customer to purchase the item for a "reliable" price.
Common = 5 Platinum Pieces
Uncommon = 25 Platinum Pieces
Rare = 250 Platinum Pieces
Very Rare = 2,500 Platinum Pieces